The most difficult part in high resolution CCTV camera surveillance used in critical infrastructure projects is the storage of incoming data from cameras, especially when a long retention period is needed. The size of the storage can be very high, even for a low number of CCTV cameras. The storage of such data depends on the following factors:
- the camera resolution
- the number of frames per second (fps)
- the scene scenario
- the compression level
The following provides examples of storage requirements when using AXIS Design Tool and provides a preferred design solution that fulfils the need for storage of high-quality CCTV images.
The camera chosen for this example is the AXIS M3106-L network camera. A total of 24 cameras are used in the example, with 3MP resolution and a retention period of 30 days. The configuration parameters, chosen to provide the best monitoring quality, are:
- frame rate: 30fps
- video encoding: H.264
- compression: 10 percent
- recording: 24 hours per day
The monitoring condition for this example is the Station monitoring scenario from AXIS Design Tool, which produces the highest amount of streaming data.
According to AXIS Design Tool, the required storage using 3MP resolution and 30-day retention is 156TB, as shown in Figure 1. This amount of data (36 hard drives x 5TB) needs to be arranged in three RAID 5 sets, with each RAID set consisting of 12 hard drives.
Dealing with critical infrastructure requires a higher level of reliability, so one CCTV data stream may not be enough. The reliability can be increased partially for the 24 cameras by implementing one of these arrangements:
- The cameras should be configurable multi-streaming cameras, with one stream for 3MP configuration and one stream for VGA configuration. The VGA resolution data stream can be stored on another server as a safe redundant solution.
- Use two sets of cameras – one set of 3MP cameras and one set of VGA cameras. The cameras are mounted in twins and each pair consists of one 3MP camera and one VGA camera side by side, with the same lens and sensor characteristics so the same area is monitored, but at different resolutions. The VGA resolution data stream can be stored on another server as a safe redundant solution.
Using the same configuration parameters as above, according to AXIS Design Tool, the required storage for 24 cameras using VGA resolution and 30-day retention is 15.2TB, as shown in Figure 2.
The number of hard disks required for the 156TB, 3MP option is 36 (5MB) arranged in three RAID 5 sets, where each RAID 5 stores 11 x 5 = 55TB. The number of hard disks required for the 15.2TB, VGA option is 5 (4MB) arranged as RAID 5, 4 x 4 = 16TB.
The second arrangement – using one 3MP resolution camera and one VGA resolution camera in each pair – is the best option for a better redundancy level.
- A server with 10–11 SSD (1TB) arranged in RAID 5 for data storage. The reason for choosing SSD is the high read/write speeds.
- In the case of low-budget conditions, one LTO-6 tape drive.
- In the case of high-budget conditions, one LTO-6 tape library that covers the retention period.
- The LTO-6 tape storage capacity is 6.25TB compressed.
- A backup program, such as Arcserve from CA.
- The server that is used for VGA resolution data storage can be used for the backup program.
The success of this method is related to the configuration of the backup software, which is the most important part in implementing this method. The backup should start after midnight by one or two hours, but this timing can be changed after testing. It should be configured to backup only the files that have been created and completed before the current date. For example, if the backup starts at 2am on 20/9/17, files up to 19/9/17 should be included in the backup; any file that is still open should not be included. The backup files should be deleted from the server (SSD RAID) and the tape should be ejected and replaced with a new one.
The New Scenario
If the same parameters as above are used again, but the retention period is changed to one day, according to AXIS Design Tool, the required storage for 24 cameras using 3MP resolution is 5.19TB, as shown in Figure 3. This is well covered by SSD hard disks 9–10TB RAID 5.
At the beginning of the day, after the data has been stored in the backup program, process the backup of the stored data into the LTO-6 tape 6.25TB compressed; the size of this data in the SSD RAID is about 5.19TB (the daily stored data). The backup program then deletes all the original files from the SSD RAID and enough storage space is ready for the new incoming data from the cameras.
To cover the storing of streamed data for the whole retention period, there should be enough tapes to cover the retention period; in case of a 30-day retention period, 30–31 tapes are required.
The benefits of this method:
- Less hard disks are required, which means lower probability of a hard disk crash and lower power consumption.
- A safe copy of the tape can be created and kept in another location.
- It is easier to restore the data information from any day for forensic requirements without affecting the data streaming into the high-end resolution server.
- The retention period can be easily extended by increasing the number of LTO tapes and the VGA resolution server storage capacity.
- The number of CCTV cameras can easily be doubled and what is required is a new SSD RAID 5 set and another LTO-6 drive with LTO-6 tape set plus a new 5 HD x 4 TB RAID 5 set.
- The quality of the stored data is at the highest level, maximum frame rate and low compression.
Lamie Saif is a communication engineer, expert in CCTV surveillance and computer networks and an inventor with two patents.